Color change cyanoacrylate adhesives

ABSTRACT

A cyanoacrylate-based adhesive composition is disclosed. The cyanoacrylate-based adhesive composition includes a cyanoacrylate monomer, and a bleachable dye including a Michler&#39;s hydrol cation or derivatized Michler&#39;s hydrol cation, paired with a non-nucleophilic anion that provides a stable color to the cyanoacrylate-based adhesive.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/824,970, filed on Sep. 8, 2006, which isincorporated by reference herein.

BACKGROUND

The present disclosure relates generally to color change cyanoacrylateadhesives and methods of using the same.

Cyanoacrylate adhesives, also known as “super glues,” are a versatilefamily of adhesives known to cure in seconds and provide strong adhesionto a wide variety of surfaces. In spite of these noteworthy attributes,several issues exist that limit the popularity of this adhesive classwith consumers.

One issue with cyanoacrylate adhesives is that these adhesives bondinstantly with skin. This issue is compounded by the fact thatcyanoacrylate adhesives are usually colorless and difficult to observewhen applied to a substrate. The inability of the end-user to observewhere the adhesive is (or is not), as well as whether the adhesive iscured, often leads to unintended bonding of skin to itself or othersubstrates.

Some cyanoacrylate adhesives are lightly tinted to provide the end-usersome ability to discriminate where the adhesive has and has not beenapplied. However, these color tints are often so light that a thinlyapplied adhesive layer is not perceptible. Increasing the intensity ofcolor tint so that the thinly applied adhesive layer is perceptible,results in the cured adhesive remaining visible on the completed projectwhich may be objectionable to the consumer.

SUMMARY

In an exemplary implementation, cyanoacrylate-based adhesivecompositions are disclosed that include a cyanoacrylate monomer and ableachable dye such as, for example, a Michler's hydrol cation orMichler's hydrol cation derivative, that provides a stable color to theuncured cyanoacrylate-based adhesive when paired with a non-nucleophilicanion.

In another exemplary implementation, the method includes combining anappropriately stabilized cyanoacrylate monomer with a bleachable dyesuch as, for example, a Michler's hydrol cation or derivatized Michler'shydrol cation paired with a non-nucleophilic anion to form a dye pair.The stabilized cyanoacrylate monomer and dye pair forms acyanoacrylate-based adhesive composition. The dye pair provides a stablecolor to the cyanoacrylate-based adhesive composition.

These and other aspects of the adhesives according to the subjectinvention will become readily apparent to those of ordinary skill in theart from the following detailed description together with the Examples.

DETAILED DESCRIPTION

Accordingly, the present disclosure is directed to color changecyanoacrylate adhesives and methods of using the same. In particular,the cyanoacrylate adhesive is colored in the uncured state and becomescolorless or light-colored upon cure. In another embodiment, thecyanoacrylate adhesive is a first color in the uncured state and changesto a second color upon cure. These color change adhesives can allow theend-user to easily observe the lay of the adhesive as it is dispensed,and additionally, affords a means of visually assessing uniformity ofbond lines, as well as determining where excess adhesive has beenapplied. These color change adhesives can allow the end-user a means ofindicating the state-of-the-cure of the adhesive. In one example, ifduring the gluing operation the adhesive is colored, it is not cured,and accordingly, when said adhesive is fully cured, it is colorless orlightly colored. Normally if exposed adhesive is colorless or lightlycolored it is sufficiently cured so that it may be touched without fearof bonding to the skin. While the present invention is not so limited,an appreciation of various aspects of the invention will be gainedthrough a discussion of the examples provided below.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the following specification and attached claimsare approximations that all variation depending upon the desirableproperties sought to be obtained by those skilled in the art utilizingthe teachings disclosed herein.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

The term “polymer” will be understood to include polymers, copolymers(e.g., polymers formed using two or more different monomers), oligomersand combinations thereof, as well as polymers, oligomers, or copolymersthat can be formed in a miscible blend.

The term “alkyl” refers to a straight or branched chain monovalenthydrocarbon radical optionally containing one or more heteroatomicsubstitutions independently selected from S, O, Si, or N. Alkyl groupsgenerally include those with one to twenty atoms or from one to tenatoms. Alkyl groups may be unsubstituted or substituted with thosesubstituents that do not interfere with the specified function of thecomposition. Substituents include alkoxy, hydroxy, mercapto, amino,alkyl substituted amino, or halo, for example. Examples of “alkyl” asused herein include, but are not limited to, methyl, ethyl, n-propyl,n-butyl, n-pentyl, isobutyl, and isopropyl, and the like.

The phrase “stable color” will be understood to mean that a color orcolor intensity that visually persists for at least 14 days as measuredby the test method described in the Examples herein. For example, aflowable cyanoacrylate adhesive is said to possess a “stable color” ifthe color or color intensity (e.g., blue color) visually persists for atleast 14 days in a sealed container. In some embodiments, the samplesremain usefully colored for a period of at least six months, or at least1 year, or at least 2 years.

Unlike conventional pH indicators which are sequentially reversible,i.e., reversing color upon sequential exposure alternately to acid andto base, the bleachable dyes of the present invention tend to bleachirreversibly when formulated in color change cyanoacrylate compositions.

The cyanoacrylate-based adhesive composition described herein includes acyanoacrylate monomer and a bleachable dye cation paired with anon-nucleophilic anion that provides the bleachable dye with a stablecolor. As this cyanoacrylate-based adhesive cures, it becomes colorlessor lightly colored. In many embodiments, the bleachable dye cationpaired with a non-nucleophilic anion is blended with the cyanoacrylatemonomer prior to being applied to a substrate. In some embodiments, thebleachable dye cation paired with a non-nucleophilic anion is notblended with the cyanoacrylate monomer before the cyanoacrylate monomeris disposed on a substrate. In these embodiments, the bleachable dyecation paired with a non-nucleophilic anion can be disposed on thesubstrate and then the cyanoacrylate monomer is disposed on thebleachable dye cation paired with a non-nucleophilic anion.

The bleachable dye cation or cations can be chosen to produce any color,as desired. In many embodiments, the bleachable dye cation produces ablue or deep blue color. In many embodiments, the bleachable dye cationis formed from a Michler's hydrol (i.e.,4,4′-bis(dimethylamino)benzhydrol) or a derivative thereof.

Michler's hydrol or 4,4′-bis(dimethylamino)benzhydrol) is commerciallyavailable (from Sigma-Aldrich, St. Louis, Mo. 63103) and has thefollowing chemical structure:

Michler's hydrol is a dye base and is colorless in its free (pure) form,and because this dye base by virtue of its amine substituents isnucleophilic, and as such will cause immediate polymerization ofcyanoacrylate monomer, it is acidified prior to introduction into thecyanoacrylate described herein. When acidified, Michler's hydrol cationprovides a blue (cyan) color: the color intensity varying with theacidified dye concentration. Selection of the appropriate acidstabilizer or non-nucleophilic anion to maintain dye (color) stabilityupon aging is described below. While not being bound by any particulartheory, it is believed that Michler's hydrol cation is a dye that isdegraded (e.g., bleached) concomitant with curing of the cyanoacrylateadhesive composition.

Derivatized Michler's hydrol can be used for the bleachable dye cation.Useful derivatized Michler's hydrols include, for example, the followingmolecules: bis[4-(4-morpholinyl)phenyl]methanol (CAS#123344-13-8) havinga chemical structure:

1,1-bis(4-dimethylaminophenyl)ethanol (CAS#33905-89-4) having a chemicalstructure:

1,1-bis(4-dimethylaminophenyl)ethylene (CAS# 22057-85-8) having achemical structure:

(It is believed that this compound is converted by proton addition tothe methylene group into the same bleachable dye cation as provided bythe preceding structure.)bis(4-dimethylamino)-2-methylphenyl)methanol)(CAS#4300146-3) having a chemical structure:

bis(3-bromo-4-dimethylaminophenyl)methanol having a chemical structure:

N-[bis(4-dimethylaminophenyl)methyl]morpholine (CAS#21295-86-3) having achemical structure:

N-[bis[4-(dimethylamino)phenyl]methyl]-N′-n-butyl-urea (CAS#27086-41-5)having a chemical structure:

N-[bis[4-(dimethylamino)phenyl]methyl]-N′-(4-ethoxyphenyl)-urea(CAS#37171-10-1) having a chemical structure:

N-[bis[4-(dimethylamino)phenyl]methyl]-N′-(4-methylphenyl)-urea (CAS#123344-13-8) having a chemical structure:

N-[bis[4-(dimethylamino)phenyl]methyl]-N′-phenyl-urea (CAS#34851-49-5)having a chemical structure:

N-[bis[4-(dimethylamino)phenyl]methyl]-aniline (CAS# 6245-51-8) having achemical structure:

N-[bis[4-(dimethylamino)phenyl]-methyl]-benzenesulfonamide (CAS#3147-38-4) having a chemical structure:

These Michler's hydrol derivatives are either commercially available ordescribed in U.S. Pat. Nos. or Publication No.: 4,407,960; 3,874,884;3,856,552; 4,006,018; 3,646,135; and 2005-1488010, all of which areincorporated by reference herein.

The bleachable dye cation can be present in the cyanoacrylate adhesivein any useful amount. In many embodiments, the bleachable dye cation canbe present in the cyanoacrylate adhesive in an amount from 1 ppm orgreater, or 10 ppm or greater, or 50 ppm or greater, or 100 ppm orgreater, or 250 ppm or greater, or 500 ppm or greater, or 1000 ppm orgreater. In some embodiments, the bleachable dye cation can be presentin the cyanoacrylate adhesive in an amount from 1 ppm to 1000 ppm, orfrom 10 to 500 ppm, or from 1 to 100 ppm.

The non-nucleophilic anion is typically derived from acids of highstrength. The strength of such acids is often classified by means ofAcidity Indicators, i.e., members of a series of increasingly weaknitrated aniline bases that provide a readily measured color change uponprotonation. The accepted measure of the “strength” of aqueous acidicsolutions is pH, the negative logarithm of the hydrogen ionconcentration (or activity), and pK_(A), which similarly is the negativelogarithm of the ionization constant K_(A). in aqueous solution, of weakto moderately strong acids. For extremely strong acids these means ofdescription fail, as strong acids react with water, acting as a base, toform hydronium ion, H₃O⁺, thus preventing the expression of higheracidities. For the measurement of the ultimate proton-donating acidityof pure anhydrous acids, the H_(o) (Hammett Acidity Function) scale wascreated (L. P. Hammett & A. J. Deyrup, J Amer. Chem. Soc., 54 2721, 4239(1932), 55 1900 (1933)). Its numerical scale was provided by stepwisedilution of each acid by water until the composition fell within themeasurable pH range, thus it was termed an extension of the pH scale.Color-indicating very weak bases were provided, for which the protonatedforms had non-aqueous pH-like behavior that could be inter-related bystepwise overlap. While useful, the H_(o) scale provides no commonnon-aqueous medium for comparisons, as each anhydrous acid differs insolvent properties. Nearly all common “good” solvents are protonated by,or are reactive toward, very strong acids. Furthermore, to retain bothneutral and ionic species in solution, a relatively high dielectricconstant is accepted as necessary. Nitromethane appeared to be such asolvent (L. C. Smith & L. P. Hammett, J Amer. Chem. Soc., 67 23 (1945)),but failed to provide simple buffer equilibria; this behavior was (andremains) unexplained.

The Hammett Acidity Function is applied to pure or nearly pure acids, asituation extremely different from the use in solution in acyanoacrylate monomer. It is appropriate therefore to evaluate acidstrengths in a polar organic solvent by a means analogous to ordinaryaqueous buffer systems, which depend on the strength of the acidsemployed.

Anhydrous “Sulfolane” (tetramethylene sulfone;tetrahydrothiophene-1,1-dioxide, CAS RN 126-33-0), is an acid-inertnon-dissociating good solvent of high dielectric constant, 44, (E. M.Arnett & C. F. Douty, J Amer. Chem. Soc., 86 409 (1964)), and has thefurther advantage that the melting point is a sensitive measure of itswater content (R. L. Burwell Jr & C. H. Langford, J Amer. Chem. Soc., 813799 (1959)). Although requiring rigorous purification to remove tracesof water, and impurities that are severely discolored by strong acids,it does appear to yield simple buffer and color-indicator equilibria.

Therefore we create the non-aqueous analog of the common buffer systemby combining equimolar amounts of a very strong acid and its salt inanhydrous sulfolane, and evaluate the buffered acid's strength by meansof an Acidity Indicator, 1. (For such an aqueous 1:1 buffer the aqueous;pH is equal to the pK_(A) for the aqueous acid.) The procedure toconduct such measurements is described in detail in the Test Methodssection of this disclosure. Strength of an acid buffer of anycomposition may for simplicity be expressed by means of the ratio ofmolar extinction coefficients, ∈, and ∈*, where ∈ is the molarextinction coefficient of an Acidity Indicator, 1, in the acid-freesolvent, sulfolane, and ∈* is the apparent molar extinction coefficientof that Acidity Indicator in a buffered test solution (as described inthe Test Methods section) according to the following equations:

Extinction Ratio=∈/∈=N and (∈−∈*)/∈=C=(1−N)

For an Equimolar (1:1) Buffer, for which the Strength Ratio, E=(∈−∈*)/∈(for a specified Acidity Indicator, I), E expresses the strength of theacid itself. To exhibit this relative to the strength of the conjugateacid, IH^(I), of the Acidity Indicator it is convenient to use thefamiliar negative logarithmic form: pA=−log(E/N)=+log(N/E).

Given a “pK_(I)” for the (conjugate acid) strength of an AcidityIndicator, the strength of a buffer's acid on that scale becomes“pK_(A)”, where “pK_(A)”=“pK_(I)”+pA. Such a single self-consistentscale is provided computationally for all of the Acidity Indicators asdescribed under Indicators in the Test Methods section.

For a workable carbon-acid the Strength Ratio, E, defined as (∈−∈*)/∈,for a chosen 1:1 buffer system in the sulfolane solvent described above,is greater than 0.1 (corresponding to “pK_(A)”<+2.0), preferably greaterthan 0.25 (corresponding to “pK_(A)”<+1.5) when the indicator I is4-methoxy-2-nitroaniline. For a workable non-carbon-acid, for example anoxyacid, the acid Strength Ratio E, as measured in the sulfolane solventdescribed above, is greater than 0.2, preferably greater than 0.5(corresponding to “pK_(A)”<−1.0), when the indicator is4-chloro-2-nitroaniline, or more preferably greater than 0.50(corresponding to “pK_(A)”<−2.3) when the indicator is2-chloro-6-nitroaniline, or even more preferably greater than 0.5(corresponding to “pK_(A)”<−5.4) when the indicator is2,6-dinitroaniline. The mathematically equivalent Acid Strength measure,“pK_(A)”, applicable to all buffer ratios, is described in the TestMethods section. It enables the Strength Ratio, E, to be ascertained bymeans of titration.

Carbon-acids differ qualitatively in being extremely much weaker thanacids bearing the acidic hydrogen on, for example, oxygen or nitrogen,as is well established in the scientific literature. It is unusual for acarbon-acid to possess sufficient acid strength to be measurable usingthe nitrated aniline Acidity Indicators utilized herein. For acarbon-acid to be this strong it is necessary that its anion benon-nucleophilic. As compared to the strong non-carbon-acids whichhomopolymerize epoxy compounds, the observation that these relativelyweaker carbon-acids also homopolymerize epoxy compounds demonstrates thecomparably non-nucleophilic nature of their anions.

The non-nucleophilic anion can include an α,β-highly fluorinated orperfluorinated(C₁-C₈)alkylsulfonate anion. In further embodiments, thenon-nucleophilic anions include those derived from bis(α,β-highlyfluorinated or perfluorinated-sulfonyl)methane, tris(α,β-highlyfluorinated or perfluorinated-alkylsulfonyl)methane, bis(α,β-highlyfluorinated or perfluorinated-alkylsulfonyl)imide, or mixtures thereof.In yet further embodiments, the non-nucleophilic anion may be formedfrom trifluoromethanesulfonic acid, nonafluorobutanesulfonic acid,fluorosulfonic acid, bis(trifluoromethanesulfonyl)methane (methylenedisulfonic), bis(trifluoromethanesulfonyl)imide (imide acid),bis(pentafluoroethanesulfonyl)imide (ethylimide acid),tris(trifluoromethanesulfonyl)methane (methide acid), boron trifluoridebis-acetic acid, and other boron trifluoride complexes such as theetherate, methanol, propanol, and tetrahydrofuran derivatives. Similarreagents that react, decompose, or hydrolyze to form any of the aboverecited acids are also useful. Combinations of the acids from which theaforementioned non-nucleophilic anions are derived may also be useful inthe practice of this invention. In some embodiments, thenon-nucleophilic anion is formed from trifluoromethanesulfonic acid,methide acid, boron trifluoride methanol, boron trifluoride bis-aceticacid, imide acid, and/or ethylimide acid. In certain preferredembodiments, the non-nucleophilic anion is formed from imide acid, borontrifluoride bis-acetic acid, and/or methide acid.

The non-nucleophilic anion can be present in the cyanoacrylate adhesivein any useful amount. In many embodiments, the acid of thenon-nucleophilic anion can be present in the cyanoacrylate adhesive inan acid/dye mol ratio from 1 to 5, or from 1 to 2.5. In certainembodiments, the acid of the non-nucleophilic anion can be present inthe cyanoacrylate adhesive in an acid/dye mol ratio from 1 to 5, or from1 to 3, or from 1.5 to 2.5. With careful formulation, the presence oflesser amounts (equivalents) of certain nucleophilic anions maysometimes be tolerated.

Cyanoacrylate adhesives described herein include, for example,2-cyanoacrylates such as, for example, methyl-2-cyanoacrylate,ethyl-2-cyanoacrylate, propyl-2-cyanoacrylate,isopropyl-2-cyanoacrylate, butyl-2-cyanoacrylate,isobutyl-2-cyanoacrylate, amyl-2-cyanoacrylate, hexyl-2-cyanoacrylate,cyclohexyl-2-cyanoacrylate, octyl-2-cyanoacrylate,2-ethylhexyl-2-cyanoacrylate, allyl-2-cyanoacrylate,propargyl-2-cyanoacrylate, phenyl-2-cyanoacrylate,benzyl-2-cyanoacrylate, methoxyethyl-2-cyanoacrylate,ethoxyethyl-2-cyanoacrylate, tetrahydrofulfuryl-2-cyanoacrylate,2-chloroethyl-2-cyanoacrylate, 3-chloropropyl-2-cyanoacrylate,2-chlorobutyl-2-cyanoacrylate, 2,2,2-trifluoroethyl-2-cyanoacrylate,hexafluoroisopropyl-2-cyanoacrylate, and/or the like. In manyembodiments, these reactants are substantially/effectively anhydrous.

The cyanoacrylate-based adhesive compositions described herein areliquid or gels (if a sufficient amount of thickener is combined) priorto curing. In many embodiments, the liquid or flowablecyanoacrylate-based adhesive compositions have a viscosity in a rangefrom 1 to 5000 cP, as desired.

The color change 2-cyanoacrylate-based adhesive composition describedherein can optionally include an additional colorant, a radicalpolymerization stabilizer, a thickener, a curing accelerator, acrosslinker, a plasticizer and/or a thixotropic agent, as desired.Desirably all additives should be substantially anhydrous and free ofnucleophilic compounds that may be deleterious to the bleachable colorstability, the viscosity stability or both. Furthermore, the selectionof the acidic compounds influence curing speed and product life of2-cyanoacrylate-based compositions. Thus, selection of their suitableamounts to be added and combination can be determined by taking intoaccount target curing performance, product life, color changeperformance and various other aspects.

The additional colorant can be provided to achieve change in colors froma first colored state to a second colored state as the color changecyanoacrylate-based adhesive progresses from an uncured state to a curedstate. The additional colorant can be any useful dye or pigment. In someembodiments the additional colorant is an indicator dye (not ableachable dye such as Michler's hydrol or derivative) that can furtherchange color as the cyanoacrylate-based adhesive progresses from anuncured state to a cured state. In some embodiments, the additionalcolorant includes two or more pigments or dyes, depending on a desiredcolor (in the cured or uncured state). The change in color of thecyanoacrylate-based adhesive from a first colored uncured state to afinal colored cured state, or from a first colored uncured state to afinal colorless cured state can be used to indicate the progress of thecuring reaction or change in the cyanoacrylate-based adhesive. Visualcolor standards may be prepared and provided as a reference to thereaction progress. For example, a simple series of three printedcolor-matched dots that diminish in intensity as the concentration ofacidified Michler's hydrol cation in the curing adhesive diminishesmight be useful in determining whether the adhesive was curing properly,and furthermore aid in identifying whether the initial composition wassufficiently unpolymerized to be a useful adhesive composition.

The radical polymerization stabilizer can include hydroquinone,hydroquinone monomethyl ether, catechol, pyrogallol and the like. Insome embodiments, the radical polymerization stabilizer can be presentin the range of 1 ppm by weight to 1% by weight.

In order to decrease bonding time, anion polymerization accelerators canbe added to uncured cyanoacrylate adhesives, which include polyalkyleneoxides and their derivatives, crown ethers and their derivatives,silacrown ethers and their derivatives, calixarene derivatives,thiacalixarene derivatives and the like, and combinations or blends ofany of the aforementioned classes of accelerators. Some usefulaccelerants are disclosed in U.S. Pat. No. 6,835,789 and incorporatedherein to the extent it does not conflict. In some embodiments, theaccelerant is present in the range from 200 to 5000 ppm. Nucleophilicpolymerization accelerators, e.g., amines such asN,N-dimethyl-p-toluidine solutions may also be applied to adherendsurfaces prior to application of an uncured cyanoacrylate adhesive inorder to accelerate cure of the adhesive.

Thermal performance of cyanoacrylate adhesives is typically improved bythe addition of crosslinkers, i.e., multi-functional monomers which uponor subsequent to cure crosslink the polymerizing adhesive. Usefulcrosslinkers may include biscyanoacrylates, allyl-2-cyanoacrylate,propargyl-2-cyanoacrylate, multi-functional acrylates and(meth)acrylates, and combinations of the aforementioned.

The thickener can include viscosity modifiers, gel formers, thixotropic,and/or polymeric additives such as, for example, polymethylmethacrylate(PMMA), methyl methacrylate/acrylate copolymers, methylmethacrylate/methacrylate copolymers, cellulose derivatives, fumedsilica, hydrophobic silica, and the like. In some embodiments, thethickener can be added in the range of 0.1 to 20% by weight. In someembodiments, the thickener can be added to provide a viscosity in arange from 5 to 5000 cP. In certain embodiments, the thickener can beadded to provide a viscosity in a range from 2500 to 100,000 cP. In someembodiments, PMMA and fumed silica are combined in the composition toform a cyanoacrylate adhesive gel.

The plasticizer can be added to adjust modulus of the adhesive from arigid adhesive to a toughened or flexible adhesive. Plasticizers caninclude, for example, phthalate esters, citrate esters, glyceroltriacetate, specific multifunctional (meth)acrylates and the like. Insome embodiments, the plasticizer can be added in the range of 0.01 to30% by weight.

In addition, perfumes, fillers, crosslinking agents, polymerizationinitiators, organic solvents or the like can optionally be added, asdesired.

The present invention should not be considered limited to the particularexamples described herein, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention can be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the instant specification.

Test Methods Set Time

Set time was determined by depositing a single drop of cyanoacrylateadhesive (hereinafter “CA”) on a glass microscope slide, overlapping asecond slide atop the first, and applying modest finger pressure on thetop slide in the bonding region to create a thin glue line. At the timethe bond line is closed (2nd slide put in place) a stop watch isstarted. While holding the 1st slide, the 2nd slide non-bonded end ismoved slowly from side to side over a small range of motion, of no morethan 30 degrees, to determine when it can no longer be moved. When slide2 can no longer be moved, the time on the stopwatch is recorded as theset time.

Color Assessment

A quantitative color assessment was performed to determine if changesoccurred in sample color over time. This quantitative assessment wasconducted by comparing the example to known colorimetric standardsconsisting of aqueous methylene blue solutions (preferably acidified byacetic acid) at concentrations of 2.0×10⁻⁴ M, 1.5×10⁻⁴ M, 1.0×10⁻⁴ M,and 0.5×10⁻⁴ M, packaged in the same quantity and bottle type as theexperimental samples. A quantitative color scale of 0, 1, 2, 2.5 and 3was employed where 3 corresponds to the deepest blue and 0 correspondsto colorless. Methylene blue concentrations of 2-, 1.5-, 1.0-, and0.5×10⁻⁴ M correspond to color ratings of 3, 2.5, 2, and 1 respectively.A colorless sample would be rated 0.

Bleaching

Bleaching was assessed at the conclusion of the set time test describedabove. In this case samples were visually inspected approximately 1 hourafter conducting the set time test and identified as either “colorless”,if they bleached colorless, or “tinted”, if color or hue remained.Results from this test are labeled “Set Time Bleach”.

Acid Strength Determination

The objective of this test method is to establish the strength of theacid being tested, as expressed, for example, in a half-neutralized“buffer” solution in purified sulfolane (tetramethylene sulfone), fromwhich the strength is revealed by UV-Vis spectrometry to determinedegree of protonation of an Acidity Indicator, 1, and expressed relativeto it as the Strength Ratio, E. More generally the mathematicallyequivalent Acid Strength, “pK_(A)”, available from buffers of allratios, or by titration, may be used to calculate the Strength Ratio.

Purification of Sulfolane

For this test method, sulfolane having a mp of at least 26.0° C., orpreferably at least 28.0° C., or more preferably greater than or equalto 28.4° C. relative to the mp of 99.999% pure gallium, 29.765° C.,(measured using a thermometer so calibrated) and being substantiallytransparent, i.e., giving a stable near-zero absorbance baseline whenthis sulfolane is present in the sample cell, with pure water in thereference cell of a double beam spectrophotometer over the region350-550 nm, is required. For this and all subsequent absorbancemeasurements the reading at 550 nm should be found to be near zero.

For this test method, not even the best commercial “Reagent” or “99+%”sulfolane is suitable. Less pure grades (if wet, they can be firstimproved by storing with KOH pellets) can be brought to “Reagent” levelby crystallizing below 20° C., then allowing to slowly melt at 25°C.-27° C. with frequent or continuous drainage of the melt liquid, whichcan be recycled. The portion remaining solid and/or the commercial“99+%” sulfolane, is subjected to the following purification regimen. Toavoid freezing of the purified sulfolane during handling, it isadvisable to maintain the work area at or above 30° C.

To a stoppered 500 ml Erlenmeyer flask, fitted with a Bunsen valve orother pressure-relief device, is placed 300 to 350 g of the “99+%”sulfolane and 1.58 g KMnO₄. The liquid, initially deep magenta, developsa brown cast (from MnO₂). It is warmed on a hot plate held at 45-55° C.for at least 5 days, with additional 1 g portions of KMnO₄ being addedas needed to maintain a weak magenta color. The liquid is decanted awayfrom any settled solids and centrifuged (filtration is difficult) toremove MnO₂. The supernatant liquid is decanted into a 500 ml Erlenmeyerflask with pressure-relief stopper, and to it is added 15 g of apreviously-prepared drying mixture, which had been made at least one dayearlier by shaking together in a well sealed bottle equal weights ofphosphorus pentoxide and 100-200 mesh silica gel that had been dried at170° C. overnight. The flask of sulfolane and drying mixture is heatedfor at least 1 week on a hot plate at 100° C. and soon turns to anamber-brown color. It is then cooled and the very dark liquid decantedinto a 250 ml distilling flask. To control “bumping” during distillationit is desirable to add 10 to 15 fluoropolymer PFA (or FEP) tubes, ofoutside diameter about 3 mm, inside diameter about 1 mm, sealed off attheir tops, and of a length greater than the flask diameter.

The flask, heated by a heating mantle, is surmounted by a simple vacuumfractional distillation unit, comprising first a short Vigreux columnsection (to intercept “bumped” liquid) and above it a section containinga 20 cm length of ¼″ Pyrex helices, or preferably a 10 cm long sectioncontaining Podbielniak™ Helipak™, ⅛″, stainless steel, either contentsbeing available from Wilmad-LabGlass, Elk Grove Village, Ill. Above itis a standard vacuum distillation head with reflux style condenser andthermometer, and stopcocks positioned to allow controlled take-off, plusexchange and re-evacuation of receptor flasks, specifically withoutbreaking the vacuum of the distillation column. Only minimal insulationof the column or head by means of a few paper towels wrapped around thehot parts is needed, with provision for observation of a tendency to“flood” in the packed section, as it may be alleviated by blowing air onthe distilling flask. The entire distilling apparatus should beassembled with 24/40 standard taper joints fitted with PTFE conicalsleeves and made vacuum tight throughout with perfluorinated vacuumgrease, available as Krytox LVP, from E. I. du Pont de Nemours andCompany, Wilmington, Del., in order to resist hot sulfolane vapor.

For vacuum distillation an ordinary oil pump capable, with liquidnitrogen trap, of exhausting the system to 0.05 Torr., is needed, toenable sulfolane to distill at 68-75° C., as much higher pressure andtemperature may produce discoloration. The system pressure iscontinuously monitored by means of an electronic vacuum gauge readingwith reasonable precision from 0.010 Torr. to 1.0 Torr. Water flowthrough the condenser must be restricted, as the distillate will freezeand plug it below 30° C., with hazardous consequences.

Distillation should become relatively stable around 73° C./0.10 Torr.,and a large center cut of 130-150 g should be taken at 72° C./0.090Torr. to 68° C./0.050 Torr. This cut, upon crystallization in its ca.150 mL receiver flask, should upon warming show melting of its lastcrystals at 2° C., or preferably 1.5° C., or more preferably 1° C. belowthe melting point of 99.999% gallium metal, 29.765° C., one of severalpure-metal melting points that officially define the Celsius temperaturescale, as explained by H. Preston-Thomas et al., Metrologia 27 3 (1990).The literature melting point, 28.86° C., given without reference to oneanother by S. F. Birch and D. T. MacAllan, J. Chem. Soc. (London) 2556(1951) and by E. V. Whitehead, R. A. Dean and F. A. Fidler, J. Amer.Chem. Soc. 73 3632 (1951), and allegedly obtained by extrapolation fromlower temperature data, is indefensible in view of direct gallium-basedmeasurement of 29.0° C. minimum.

Sulfolane has a low heat of fusion, as given by R. L Burwell Jr. and C.H. Langford, J. Amer. Chem. Soc., 81 3799 (1959), and therefore has anextremely large freezing point depression, thus providing an upper limiton water content, increasing by 0.031 m in water content for each 1.00°C. reduction in melting point.

Nevertheless, sulfolane does not have to be treated with excessive care,as it is virtually nonvolatile at atmospheric pressure, thus cannotcondense moisture by evaporative cooling, nor lose weight byevaporation, when handled briefly in open vials. Little or no water isabsorbed from the air, as shown by slow change at the 0.01 mg level ofweight of an open vial of sulfolane on the balance. The measurable,although not large, effect on spectroscopic acidity measurementsproduced by addition of 1 microliter of water (ca. 1.00 mg), to a testsample of approximately 2.5 g, permits ready estimation of thenegligible effect of brief unprotected exposure of samples to air at 30°C. and 20 to 40% relative humidity.

Acidity Indicators

For the purpose of this work, visibly colored neutral Acidity Indicatormolecules which lose color reversibly upon accepting a proton from astrong acid are used. To minimize inconsistency of electronic effects,the selection is restricted to various substituted 2-nitroanilines, forwhich a second nitro group, if present, must be in the 6-position. It isa characteristic shared by all members of this group thus far examinedthat the neutral form has a clean symmetrical absorbance peak in therange 380-460 nm, which disappears (reversibly) for its protonated form.Thus, the fractional loss in intensity represents the reduction inconcentration of the neutral Acidity Indicator, (1), the reductionrepresenting (IH⁺). This is readily measured by a spectrophotometer, oreven by a properly filtered colorimeter.

In principle all Acidity Indicators might have their indicator constantsin sulfolane related by the stepwise overlap method as has been done,and variously revised, for measuring H_(o) as reported in the citedreferences.

-   M. A. Paul & F. A. Long, Chem. Rev. 57 1 (1957)-   M. J. Jorgenson & D. R. Hartter, J. Amer. Chem. Soc., 85 878 (1963)-   E. M. Arnett & G. W. Mach, J. Amer. Chem. Soc., 86 2671 (1964)-   N. C. Marziano, G. C. Cimino, & R. C. Passerini, J. Chem. Soc.    (London) Perkin 11, 1915 (1973)-   D. Farcasiu & A. Ghenciu, J. Prog. Nucl. Mag. Spect. 29 129 (1996)

In practice that approach is narrow in scope and suffers from cumulativeprocedural and experimental variability. An alternative system, usedhere, which is entirely objective, self-consistent and reproducible,relies experimentally on the effects of acidity on chosen specifiedAcidity Indicators. For convenience, these may be related numerically bymeans of their computed “pK_(A)” values, which may be generated for allknown and predicted 2-nitroaniline derivatives by employing acomputational method provided by Advanced Chemistry Development, Inc(ACD/Labs), Toronto, ON, Canada, www.acdlabs.com. This software isACD/pK_(a) Batch, version 9-04, ACD/Labs (©1994-2007. (Identical“pK_(A)” values were generated by their Versions 8-14 and 8-19). The“pK_(A)” values may be accessed through the Chemical Abstracts Service.These Acidity Indicator “pK_(A)” values are here termed “pK_(I)” forclarity.

Experimental spectrophotometric data are used to calculate logarithmicacidity values (“pH”, analogous to pH) that are helpful in determining Eby titration. To avoid confusion with aqueous pH and pK values, and withthe many literature H_(o) values which they resemble, the logarithmicacidity values in anhydrous sulfolane are designated “pH”, and thederived acid strength constants “pK_(A)”. One may identify theindicator(s) on which the “pK_(A)” are based, by virtue of being closeto their computational “pK_(I)” values.

The indicators chosen for the present work, together with theircomputational “pK_(I)” values are shown in Table A.

TABLE A Chosen Acidity Indicators and Their Computed “pK_(I)” ValuesChemical Name CAS Ref. No. “pK_(I)” 4-Methoxy-2-nitroaniline 96-96-80.96 4-Methyl-2-nitroaniline 89-62-3 0.46 2-Nitroaniline* 88-74-4 −0.234-Chloro-2-nitroaniline* 89-63-4 −1.00 5-Bromo-2-nitroaniline 5228-61-5−1.53 2-Chloro-6-nitroaniline* 769-11-9 −2.342,4-Dichloro-6-nitroaniline* 2683-43-4 −3.084-(Methylsulfonyl)-2-nitroaniline 21731-56-6 −3.882-Chloro-6-nitro-4-(trifluoromethyl)aniline 57729-79-0 −4.622-Bromo-6-nitro-4-(trifluoromethyl)aniline 113170-71-1 −4.742,6-Dinitroaniline* 606-22-4 −5.45 4-Chloro-2,6-dinitroaniline*5388-62-5 −6.03 2,6-Dinitro-4-(trifluoromethyl)aniline 445-66-9 −7.422,6-Dinitro-4-(methylsulfonyl)aniline 42760-39-4 −8.88

To minimize the effects of spectrophotometric uncertainty at theextremes, it is strongly recommended that the absorbance measurementsfall between 15% and 75% of the value expected if the indicator werecompletely non-protonated, i.e., in its neutral form. For the sixindicators identified with an asterisk in Table X, the computed “pK_(I)”values differ only by about 0.1 pK_(A) unit from the experimentallymeasured (and revised) pK_(A) values reported in the literaturereferences cited above, thus supporting the validity of thecomputational method. Additional computed “pK_(I)” values for indicatorspresumed to be useful are listed in Table B.

TABLE B Additional Acidity Indicators Presumed Useful and Their “pK_(I)”Values Chemical Name CAS Ref. No. “pK_(I)” 2,4-Dimethoxy-6-nitroaniline57715-92-1 0.87 2,4-Dimethyl-6-nitroaniline 1635-84-3 0.274-(Methylthio)-2-nitroaniline 23153-09-5 −0.09 2-Methoxy-6-nitroaniline16554-45-3 −0.35 2-Methyl-6-nitroaniline 570-24-1 −0.443-(Methylthio)-2-nitroaniline 351458-30-5 −0.86 4-Bromo-2-nitroaniline875-51-4 −1.05 4-Chloro-2-methoxy-6-nitroaniline 859877-49-9 −1.092-Chloro-4-methoxy-6-nitroaniline 29105-95-1 −1.124-Bromo-2-methoxy-6-nitroaniline 77333-45-0 −1.142-Bromo-4-methoxy-6-nitroaniline 10172-35-7 −1.242-(Methylthio)-6-nitroaniline 494226-39-0 −1.362-Nitro-4-(trifluoromethoxy)aniline 2267-23-4 −1.385-Chloro-2-nitroaniline 1635-61-6 −1.462-Nitro-4(trifluoromethylthio)aniline 404-74-0 −2.342-Bromo-6-nitroaniline 59255-95-7 −2.462-Nitro-4-(trifluoromethyl)aniline 400-98-6 −2.542-Nitro-6-(trifluoromethoxy)aniline 235101-48-1 −2.552,4-Dibromo-6-nitroaniline 827-23-6 −3.252-Nitro-6-(trifluoromethyl)aniline 24821-17-8 −3.372,6-Dinitro-4-methoxyaniline 5350-56-1 −4.66 2,6-Dinitro-4-methylaniline6393-42-6 −4.93 2-Nitro-4-(trifluoromethylsulfonyl)aniline 400-23-7−5.30 4-Bromo-2,6-dinitroaniline 62554-90-9 −6.214-Cyano-2,6-dinitroaniline 61313-43-7 −8.48 2,4,6-Trinitroaniline489-98-5 −9.30 2,6-Dinitro-4-(trifluoromethylsulfonyl)aniline 19822-30-1−10.40Calculations of “pH” and “pK_(A)” Values

The straightforward method of L. C. Smith and L. P. Hammett, J Amer.Chem. Soc. 67 23 (1945), is used to calculate “pH” and “pK_(A)” for thesystems of interest. For each Acidity Indicator chosen the MolarExtinction Coefficient, ∈, is calculated from the absorbance of itssulfolane solution, preferably made up exactly as for the aciditymeasurement, but omitting the acid. The equation then takes the form:

∈=AMG/SUD=AYG/U

where:

A=Absorbance measured

M=Molecular weight of the indicator

G=Weight in grams of sample solution

S=Weight fraction of solid indicator in its sulfolane concentrate

U=Weight in mg of indicator concentrate used

D=Density of the sample solution, normally 1.2622

Y=Batch constant for an indicator concentrate (=M/SD)

The needed density of the reference solution is most easily establishedby use of a small Ostwald-Sprengel pycnometer of approximately 0.5 to 2ml volume which has been calibrated against water. To fill thepycnometer by suction its tip may be dipped into the test solution inthe cell after the spectral measurement has been made.

For a sample including an acid (or its buffer) its apparent extinctioncoefficient, ∈*, is related to its observed absorbance, A*, by the sameequation. The fraction of neutral indicator (I) remaining is N=∈*/∈, andthe corresponding fraction of its conjugate acid (IH⁺) isC=(1−N)=(∈−∈*)/∈.

The acidity “pH” is given by: “pH”=“pK_(I)”+log(N/C) where “pK_(I)” isthe computed “pK_(A)” for the indicator, generated by ACD/Labs softwareVersion 9-04, as cited above.

For a titration or buffer solution, comprising B millimoles of base andF millimoles of non-neutralized “free” acid, F=T−B, T being the totalmillimoles of acid used (if B is added as the salt of T, thus notneutralizing T, F=T). From this, the “pK_(A)” for the acid is:“pK_(A)”=“pH”+log(F/B)

This, together with the preceding equations, constitutes themathematical interconvertibility of the Acid Strength, “pK_(A)”, and theStrength Ratio, E. The Strength Ratio, E, is based upon experimentallyknown ratios, FIB, resulting from accurate weighings and the presumptionthat the molality of T is correct. If the acid of T is significantlyimpure, corrections must be made. For an inert impurity the value of Tis simply reduced to T′, and F′=T′−B. If, however, as is often the case,the impurity is the salt of the acid (typically the hydronium salt,H₃O⁺A⁻) then this must also be part of the total base, B′=B+(T−T′) andthe ratio becomes:

Ratio=F′/B′=F′/(B+T−T′)=(T′−B)/(B+T−T′)

For a given very strong acid sample, originally “pure” (free frommetallic salts, etc) the existing impurity is normally water. Theeffective purity, T′/T, may be estimated by (gravimetric) titration inanhydrous sulfolane with an anhydrous weighable base. Note that unknownbut limited amounts of water present in the sulfolane will partially“neutralize” a very strong acid and modify the titration and “pK_(A)”calculation accordingly, but will not change the validity of theresulting “pK_(A)”.

In order to find the half-neutralized “1:1 Buffer” mid-point, at which Eis defined, one needs to ascertain the end-point with reasonableconfidence. This requires an indicator having a “pK_(A)” two or threeunits less acidic than “pH” measured for a (supposedly) equimolalbuffer, such that the titrated “pH” is within (passes through) the“best” indicator range, namely N=∈*/∈ between 0.15 and 0.75. Such anend-point is reliable.

Imidazole, readily soluble in sulfolane, is normally an excellent choiceas the titration or buffer-making base. Results agree with those fromethyldiisopropylamine, despite the latter's volatility and its verylimited solubility in sulfolane. They also agree with those from theadditive bases, CF₃SO₃ ⁻Na⁻ and CF₃SO₃ ⁻ (Bu₄N)⁺, these of course beinglimited to CF₃SO₃H. In view of its low molecular weight, a 1.000 molalconcentrate of imidazole in sulfolane is recommended.

Acidity measurements are best made with F and B about 0.1 nm or lower,for solubility reasons and to keep the sulfolane, as the solvent medium,in great excess. At greater dilution of very strong acids, extremely drysulfolane is needed to minimize interference.

A list of “pK_(A)” values thus measured for acids of interest instabilization of bleachably-colored cyanoacrylate adhesives is in TableC.

TABLE C Acid Strength, “pK_(A)” Chemical Structure “pK_(A)” 95%Confidence Limits (CF₃SO₂)₂NH −6.6 ±0.2 (C₂F₅SO₂)₂NH −6.6 ±0.5 CF₃SO₃H−6.1 ±0.5 BF₃•2 CH₃CO₂H −3.0 ±0.1 BF₃•2 CH₃OH −0.5 ±0.02 BF₃•2 H₂O −0.2±0.1 CH₃SO₃H 1.26 ±0.06 CF₃CO₂H 3.15 ±0.06 (CF₃SO₂)₃C⁻(H₂O)₁₆H¹ 0.93±0.30 (CF₃SO₂)₂C(H)C₆H₅ 0.97 ±0.04 (CF₃SO₂)₂CH₂ 1.32 ±0.06

Use of Titration to Determine Acid Strength, “pK_(A)”, of a Strong Acid,and Consequent Strength Ratios. The Strength Ratio, E, defined as(∈−∈*)/∈ for a chosen 1:1 buffer system, HA:A⁻, plus indicator IH⁻:I, insulfolane solvent, is not correct unless the true concentrations of HAand A⁻ are known to be equal. This is best ascertained and verified bygravimetric-spectrophotometric titration, to determine the trueconcentration of the strong acid component in the measurement sample, asdescribed below.

A stock solution is made from 0.28133 g of pure, colorless sublimedcrystals of methylene disulfone, MDS, and sulfolane to total 9.99476 g.In a stoppered 1 cm fused silica spectrophotometric cell is placed2.41146 g. of the stock solution. It contains 67.877 mg (T=0.24228 mmol)of MDS, plus 23.29 mg indicator concentrate, U, to total G grams. Theindicator concentrate is made by dissolving 6.07 mg of4-Methoxy-2-nitroaniline (molecular wt. M=168.15, “pK_(I)”=+0.96) insulfolane to total 2193.78 mg, giving S=0.002767 and thus Y=48147. (The∈ value of this indicator was determined to be 5497 by spectrophotometryon a diluted solution in sulfolane.) The absorbance at the indicator'sspectral maximum, 446 nm, is only 0.022, relative to the reference cellcontaining only the stock solution.

Titration is begun by adding a small drop, 14.46 mg, of 1.0000 msulfolane solution of purified imidazole, which thus adds 0.01446 mmolof base, B, producing absorbance 0.158. Additional increments of theimidazole solution are added, with the results shown in Table D.

TABLE D Results of Titration to Determine E for MDS Increment # &imidazole Total g Total mmol C = “pK_(A)” (mg) in cell, G (= g) of BRatio B/T Absorbance A (ε − ε*)/ε “pH” (MDS) 1 (14.46) 2.44914 0.014460.0597 0.158 0.8545 0.19? 1.39? 2 (18.26) 2.46740 0.03272 0.1351 0.2840.7365 0.51 1.32 3 (20.72) 2.48812 0.05344 0.2206 0.396 0.6295 0.73 1.284 (21.28) 2.50940 0.07472 0.3084 0.495 0.5329 0.90 1.25 5 (30.21)2.53961 0.10493 0.4331 0.610 0.4174 1.10 1.22 6 (44.44) 2.58405 0.149370.6165 0.757 0.2644 1.40 1.20 7 (50.31) 2.63436 0.19968 0.8242 0.8910.1173 1.84 1.17 8 (21.04) 2.65540 0.22072 0.9110 0.948 0.0533 2.21?1.20? 9 (25.62) 2.68102 0.24634 1.0168 0.983 0.0089 3.01?? (—) ? —indicates substantial uncertainty resulting from the extreme absorbances

The average of the six most reliable “pK_(A)” values is 1.24±0.05 (95%confidence limits). The sudden increase in “pH” signals the end-point ofthe titration, which is seen to occur at B/T=1.0 as expected for a pureacid. The mid-point (buffer ratio 1:1) most reliable value for theStrength Ratio, E=0.34, is calculated from “pK_(A)”=1.24, and“pK_(I)”=0.96 by the equation: E=1/[1+antilog(“pK_(A)”−“pK_(I)”)]. (Byinterpolation of C values, E may be approximated as 0.36.)

Materials

Unless otherwise noted, all materials were or can be obtained fromSigma-Aldrich Corp., St. Louis Mo.

“PR01” refers to 2-ethylcyanoacrylate, 100 cP, super fast cure, 10-30second set time, available from Chemence, Inc., Alpharetta, Ga. 30005.

“SB20” refers to 2-ethylcyanoacrylate, 5 cP, ethyl hybrid, 0-20 sec settime, high strength bonds on acidic surfaces, available from Chemence,Inc., Alpharetta, Ga. 30005.

“SB14” refers to 2-ethylcyanoacrylate, 100 cP, 10-60 second set time,high strength bonds on plastic and rubber, available from Chemence,Inc., Alpharetta, Ga. 30005.

“RX-100” refers to 2-ethylcyanoacrylate, 100 cP, non-surface sensitive,10-30 sec set time, available from Pacer Technology, Rancho Cucamonga,Calif. 91730.

“TX-100” refers to 2-ethylcyanoacrylate, 100 cP, 10-30 sec set time,available from Pacer Technology, Rancho Cucamonga, Calif. 91730.

“NO100” refers to 2-methoxy-ethoxy-α-cyanoacrylate, 100 cP, no odor, nofrost, 30-50 sec set time, available from Pacer Technology, RanchoCucamonga, Calif. 91730.

“HC150” refers to 2-isopropylcyanoacrylate, 150 cP, low chlorosis, highclarity, better moisture resistant than ethylcyanoacrylates, 10-30 secset time, available from Pacer Technology, Rancho Cucamonga, Calif.91730.

Scotchweld cyanoacrylate adhesives, available from 3M, Maplewood, Minn.55144 are listed in Table E below:

TABLE E Scotchweld Cyanoacrylate Adhesives Viscosity Set Time ProductChemistry (cP) (sec) Scotchweld ™ CA-40 2-ethylcyanoacrylate  2-10 1-30Scotchweld ™ CA-4 2-ethylcyanoacrylate  60-120 5-40 Scotchweld ™ CA-40H2-ethylcyanoacrylate 400-600 5-40 Scotchweld ™ CA-5 2-ethylcyanoacrylate2000-3000 20-70  Scotchweld ™ CA-7 2-methylcyanoacrylate 15-40 1-30Scotchweld ™ CA-8 2-ethylcyanoacrylate  70-120 5-40 Scotchweld ™ CA-92-ethylcyanoacrylate 1000-1700 20-70  Scotchweld ™ CA-1002-ethylcyanoacrylate 2500-4500 20-70  Scotchweld ™ CA-502-ethylcyanoacrylate gel 60-120

Scotch™ Super Glue Liquid, catalog number AD110, 2-ethylcyanoacrylate,available from 3M, St Paul, Minn., 55144.

“Nexcare™ props Liquid Bandage”, n-butyl cyanoacrylate, 5 cP, 30-60 secset time, available from 3M, St. Paul, Minn. 55144

Michler's hydrol, recrystallized from toluene, mp 102-102.5° C.,available from Sigma-Aldrich, St. Louis, Mo. 63103.

Bis(trifluoromethanesulfonyl)methane “methylene disulfone” “MDS”,synthesized using the procedures disclosed in U.S. Pat. No. 3,776,950.

Bis(trifluoromethanesulfonyl)imide “imide acid”, synthesized using theprocedures disclosed in U.S. Pat. No. 5,874,616.

Bis(pentafluoroethanesulfonyl)imide “ethylimide acid”, synthesized usingthe procedures disclosed in U.S. Pat. No. 5,874,616.

Trifluoromethanesulfonylamide “sulfonyl amide”, synthesized using theprocedures disclosed in U.S. Pat. No. 5,874,616.

Tris(trifluoromethanesulfonyl)methane, “methide acid”, 58.4% solidsaqueous, synthesized using the procedures disclosed in U.S. Pat. No.5,554,664.

Boron trifluoride-methanol complex in excess methanol, about 50 wt %BF₃, (corresponding to BF₃:2CH₃OH) available from Sigma-Aldrich Corp.,St. Louis Mo.

Boron trifluoride-acetic acid complex, 98%, available from Sigma-AldrichCorp., St. Louis Mo.

Bis-(3-bromo-4-dimethylaminophenyl)methanol—The ketone,4,4′-bis-(dimethylamino)-3,3′-dibromobenzophenone (E. Grimaux, ComptesRendus de l'Academie des Sciences, 126 1117-1118, [1898]; ChemischesCentralblatt [SF., 2J.] 1898, I, p. 1105), is reduced using 3% sodiummercury amalgam in aq. ethanol by the method of C. C. Barker et al., J.Chem. Soc. (London), 3962-63 [1959], to givebis-(3-bromo-4-dimethylaminophenyl)methanol. This product gives anintense blue color upon dissolution in acetic acid, as shown by Barkeret al., on p. 3963, thus verifying reduction of ketone to hydroxyl. Thestructure is further confirmed by NMR.

Dye base concentrate A—9 pt methyl acetate and 1 pt Michler's hydrol.

“MSA Concentrate”—solution consisting of 1.8 pt PR01 and 0.2 ptmethanesulfonic acid.

“TFMSA Concentrate”—solution consisting of 1.8 pt PR01 and 0.2 pttriflic acid (i.e., trifluoromethanesulfonic acid).

Microscope slide, VWR Cat #48300-025, selected precleaned, 25×75×1 mmthick.

Lexan™ polycarbonate sheeting 2.9 mm thick, cut into 26.5 mm×103 mmcoupons, available from GE Plastics, Pittsfield, Mass. 01201.

Pronto™ Surface Activator, acetone solution of N,N-dimethyl-p-toluidine,available from 3M, St. Paul, Minn. 55144.

EXAMPLES

Unless otherwise noted, all example formulations are provided in partsby weight.

Example 1 and Comparative Example 1

A variety of commercially available cyanoacrylate compositions wereconverted to colored-cure indicating compositions by adding a dyemasterbatch to each. The dye masterbatch was prepared by firstformulating a 10 wt % dye base solution of Michler's hydrol in ethylacetate and a 10 wt % acid solution of triflic acid in PR01. The 10 wt %dye base solution contained 1.35 part (“pt”) ethyl acetate and 0.15 ptMichler's hydrol. The acid solution contained 1.8 pt PR01 and 0.2 pttriflic acid. The dye masterbatch was prepared by combining 9.4 pt PR01,0.366 pt 10% triflic acid solution, and mixing well, before adding 0.3pt 10% dye base solution and mixing to complete the preparation andobtain a dye masterbatch having an acid/dye mol ratio of approximately2.2/1 which contained approximately 3000 ppm dye. The final samples weremade by combining, in a HDPE bottle, 0.25 pt of the dye masterbatch with10 pt of the commercial cyanoacrylates shown in Table 1 to providesamples having a final dye content of approximately 75 ppm.

The resulting samples were all deep blue in color. Set time was assessedas described in the Test Methods section, and shows that set time isessentially unaltered in these compositions by the addition of the dyemasterbatch. In the set time test all of the samples bleached from deepblue to colorless upon cure. These results show that acid/dyecombinations of the present invention are suitable to convert a widevariety of commercially available cyanoacrylate adhesive into colorchange compositions.

TABLE 1 Set time of Color Change Cyanoacrylate Adhesives Sample Set TimeSet Time Example Commercial CA No Dye Dyed Bleach 1A Scotchweld CA40 11-2 colorless 1B Scotchweld CA4 7 4 colorless 1C Scotchweld CA40H 4 3-4colorless 1D Scotchweld CA5 18-20 17-20 colorless 1E Scotchweld CA7 1 1colorless 1F Scotchweld CA8 2-3 3 colorless 1G Scotchweld CA9 5-7 5colorless 1H Scotchweld CA100 35 35-40 colorless 1I PR01 7 7 colorless1J RX-100 3-4 3-4 colorless 1K TX-100 3-4 5 colorless 1L NO-100 20 11-15 colorless 1M HC-150 25-35 30-60 colorless

Comparative Example 1 demonstrates that upon cure, pentamethoxy red(PMR), one of the dyes of US 2004/0254272 A1, does not bleach to acolorless form when employed as shown in Example 1. A 2% solution of PMRin ethyl acetate was prepared and 0.25 pt of this PMR solution was addedto 9.75 Pt PR01 to provide solution PMR-CA containing approximately 500ppm PMR dye in PR01. Upon standing for 15 minutes sample PMR-CAthickened considerably, in 30 minutes was completely gelled, and in 2 hrwas solid. This result shows that such a solution can not be madewithout adding a complementary charge of acid to the system forstability purposes.

To circumvent gelation of the dye masterbatch, a PMR dye concentratemasterbatch was made by stabilizing PR01 with triflic acid prior tointroducing the PMR dye. In this preparation a 10% PMR solution, PMR-0,was prepared by combining 1.35 pt methyl acetate and 0.15 pt PMR. PR01,TFMSA Concentrate, and PMR-10 were combined in a ratio 9.58 pt to 0.165pt to 0.3 pt respectively to create a dye concentrate, PMR-3000, havingan acid/dye molar ratio of approximately 1.5/1 and containingapproximately 3000 ppm dye. This solution was made by first combiningPR01 and TFMSA Concentrate in a HDPE container and mixing well to obtaina homogenous solution followed by addition of the PMR-10 solution andadditional mixing to homogeneity. Dye masterbatch PMR-3000 was furtherdiluted with PR01 to provide sample PMR-500, containing approximately500 ppm PMR, by combining 8.34 pt PR01 and 1.66 pt PMR-3000 and mixingto homogeneity.

Final samples were prepared as in Example 1 by adding 0.5 pt PMR-500solution to 4.5 g of the various Scotchweld cyanoacrylates and PR01,shown in Table C1, to provide comparative examples having a dye contentof approximately 50 ppm. All of the resulting comparative samples werepurple in color, and were tested for initial set time and bleaching asdescribed in the Test Methods section. The results are presented inTable C1, which show that although set times of all the samples aregenerally reasonable, perhaps some of the samples exhibit a slowing ofcure, none of these PMR-containing comparative samples bleachedcolorless upon cure, i.e., all the examples retained a purple tint aftercure. This is in contrast to the samples prepared in Example 1, based onMichler's hydrol, where upon cure all samples bleached completely in theset time test.

TABLE C1 Set time of Pentamethoxy Red Containing Cyanoacrylate AdhesivesInitial Set Set Time Example Commercial CA Time (sec) Bleach C1AScotchweld CA40 2 tinted C1B Scotchweld CA4 4 tinted C1C ScotchweldCA40H 4 tinted C1D Scotchweld CA5 9 tinted C1E Scotchweld CA7 2 tintedC1F Scotchweld CA8 4 tinted C1G Scotchweld CA9 20-30 tinted C1HScotchweld CA100 >60  tinted C1I PR01 7 tinted

Example 2 and Comparative Example 2

This example examines the solution and color stability of color changecyanoacrylate compositions based on a variety of different organic andfluorochemical acids. Dye masterbatches employing each acidwere-prepared by first formulating a 10% solution of each acid in PR01.The acid solutions contained the components and quantities shown inTable 2 (in parts by weight).

TABLE 2 Acid Concentrates Acid PR01 Acid borontrifluoride etherate 1.350.15 trifluoromethanesulfonic acid 1.35 0.15 methylene disulfone 1.350.15 methide acid 1.24 0.26 imide acid 1.35 0.15 ethylimide acid 1.350.15 trifluoromethanesulfonic anhydride 1.35 0.15 trifluoroacetic acid1.35 0.15 trichloroacetic acid 1.35 0.15 sulfuric acid (96%) 1.35 0.15hydrochloric acid (36%) 1.08 0.42 phosphoric acid (85%) 1.32 0.18 nitricacid (69%) 1.35 0.15 sulfonyl amide 1.35 0.15 methanesulfonic acid (98%)1.35 0.15 dodecylbenzenesulfonic acid 1.35 0.15

The acid concentrates prepared in Table 2 were mixed with PR01 and dyebase concentrate A in the proportions (in parts by weight) shown inTable 3 to prepare dye masterbatches. This was accomplished by addingthe acid concentrate to PR01 in a HDPE bottle and mixing well for 15minutes on a rotary agitator prior to introducing the dye concentrate.Following the addition of dye base concentrate the samples were placedback on the rotary agitator and allowed to mix at ambient temperature.All of the samples were charged to provide a dye concentration ofapproximately 3000 ppm and an acid/dye mol ratio of approximately ˜2/1,with the exception of trifluoromethanesulfonic anhydride which had a 1/1anhydride/dye mol ratio. Inspecting the samples after 30 minutes ofmixing revealed that Comparative Examples C2A-Master through C2G-Masterhad all either solidified or gelled, and thus were discarded. Withrespect to C2A-Master and C2B-Master the anions of the acids alone aretoo nucleophilic, and therefore cause gelling. In the cases ofComparative Examples C2C-Master through C2F-Master, containing water,when compared to 2D-Master containing about 40% water, which did notcause gelling, it is apparent that the anions of the acids employed inMastersC2C-Master through C2F-Master were the causes of gelling, not thewater content. Regarding C2G-Master, although slightly acidic, it failsto stabilize the dye, in contrast to its imide acid, 2E-Master. Withrespect to C21-Master, it is considered to closely resemble C2H-Masterwith respect to nucleophilicity of its anion. It is expected that otherfluorine-free organic sulfonic acids will be equivalent to these inanion nucleophilicity.

TABLE 3 Dye Masterbatches Acid Dye Base Example Acid PR01 ConcentrateConcentrate A 2A-Master borontrifluoride 4.723 0.157 0.15 etherate2B-Master trifluoromethane- 4.715 0.167 0.15 sulfonic acid 2C-Mastermethylene disulfone 4.585 0.311 0.15 2D-Master methide acid 4.453 0.4570.15 2E-Master imide acid 4.584 0.312 0.15 2F-Master ethylimide acid4.484 0.423 0.15 2G-Master trifluoromethane- 4.724 0.157 0.15 sulfonicanhydride C2A-Master Trifluoroacetic acid 4.751 0.127 0.15 C2B-MasterTrichloroacetic acid 4.702 0.181 0.15 C2C-Master sulfuric acid (96%)4.767 0.109 0.15 C2D-Master hydrochloric acid 4.829 0.040 0.15 (36%)C2E-Master phosphoric acid 4.767 0.109 0.15 (85%) C2F-Master nitric acid(69%) 4.802 0.070 0.15 C2G-Master sulfonyl amide 4.716 0.165 0.15C2H-Master methanesulfonic 4.769 0.107 0.15 acid (98%) C2I-Masterdodecylbenzene- 4.539 0.362 0.15 sulfonic acid

The remaining dye masterbatches were all deep blue colored fluids andwere further employed to formulate colored cure indicating cyanoacrylatecompositions by mixing 0.25 pt dye masterbatch with 9.75 pt PR01, asdescribed in Example I to provide samples having a final dye content ofapproximately 75 ppm. The resulting samples were divided into equalportions in separate HDPE bottles and one aged at ambient conditions andthe other at 49° C. As the samples aged, qualitative viscosityobservations were made to determine if viscosity was stable orincreasing, by inverting the bottle and observing the adhesive flow.Color of the samples was also monitored during aging, as described inthe Test Methods section of this document. The viscosity and colorassessment results are shown in Tables 4 through 7. Set time data wasmonitored periodically and results obtained reported in Table 8.

TABLE 4 Viscosity of Color Change CAs Aged at 49° C. Example Parent Acid3 day 7 day 14 day 28 day 56 day 2A boron trifluoride etherate liquidLiquid liquid no flow gel 2B trifluoromethanesulfonic liquid Liquidliquid liquid liquid acid 2C methylene disulfone liquid Liquid liquidliquid liquid 2D methide acid liquid liquid liquid liquid liquid 2Eimide acid liquid liquid liquid liquid liquid 2F ethylimide acid liquidliquid liquid liquid liquid 2G trifluoromethanesulfonic liquid liquidliquid liquid viscous anhydride C2H methanesulfonic acid solid solid — —— C2I dodecylbenzenesulfonic acid hi visc solid — — —

TABLE 5 Viscosity of Color change CAs Aged at Room Temperature ExampleParent Acid 3 day 7 day 14 day 28 day 56 day 2A boron trifluorideetherate liquid liquid liquid no flow solid 2B trifluoromethanesulfonicacid liquid liquid liquid liquid liquid 2C methylene disulfone liquidliquid liquid liquid liquid 2D methide acid liquid liquid liquid liquidliquid 2E imide acid liquid liquid liquid liquid liquid 2F ethylimideacid liquid liquid liquid liquid liquid 2G trifluoromethanesulfonicliquid liquid liquid liquid gel anhydride C2H methanesulfonic acidliquid hi visc no flow — — C2I dodecylbenzenesulfonic acid liquid slightvisc slow flow — — increase

TABLE 6 Color Stability of Color Change CAs Aged at Room Temperature 1428 56 Example Parent Acid Initial 7 day day day day 2A boron trifluorideetherate 3.00 3.00 3.00 0 0 2B trifluoromethanesulfonic 3.00 3.00 3.003.00 1.50 acid 2C methylene disulfone 3.00 3.00 3.00 3.00 2.50 2Dmethide acid 2.75 3.00 2.50 2.25 1.50 2E imide acid 3.00 3.00 3.00 3.002.50 2F ethylimide acid 3.00 3.00 3.00 3.00 2.50 2Gtrifluoromethanesulfonic 3.00 3.00 3.00 3.00 0.00 anhydride C2Hmethanesulfonic acid 3.00 0.00 0.00 — — C2I dodecylbenzenesulfonic 3.000.50 0.00 — — acid

TABLE 7 Color Stability of Color change CAs Aged at 49° C. 14 28 56Example Parent Acid Initial 7 day day day day 2A boron trifluoride 3.003.00 3.00 1 0 etherate 2B trifluoromethanesulfonic 3.00 3.00 3.00 3.002.00 acid 2C methylene disulfone 3.00 3.00 3.00 3.00 2.50 2D methideacid 2.75 3.00 2.50 2.25 2.00 2E imide acid 3.00 3.00 3.00 3.00 2.50 2Fethylimide acid 3.00 3.00 3.00 3.00 2.50 2G trifluoromethanesulfonic3.00 3.00 3.00 3.00 0 anhydride C2H methanesulfonic acid 3.00 0.00 — — —C2I dodecylbenzenesulfonic 3.00 0.00 — — — acid

The results in Tables 4 through 7 show that Comparative Examples C2H andC2I provide only limited stability as both of these Examples cured inthe bottle during heat aging, in less than 7 days, and likewise losttheir color in both room temperature and 49° C. aging.

Set time of the liquid samples aged at room temperature and 49° C. arepresented in Table 8. A control sample of PR01 had an initial set timeof 5-6 seconds and as room temperature aging proceeded, at all testtimes between 14 and 56 days, a set time of approximately 3 seconds wasobserved. The data in Table 8 show that commercial cyanoacrylatecontaining dye masterbatches based on a variety of acids, cured the sameas the control from which they were formulated, thus the presence of thedye masterbatch in PR01 did not alter cure speed. All of these inventivesamples bleached from deep blue to colorless as they cured in the settime test.

TABLE 8 Set Time of Color-Change Cyanoacrylate Samples Aged at RoomTemperature and 49° C. Set Time (sec) Set Time (sec) after after RTAging 120° F. Aging Sample 14 28 56 14 28 ID Stabilizing Acid Initialday day day day day 56 day 2A boron trifluoride etherate 5-6 3 — — 4 — —2B trifluoromethanesulfonic 5-6 3 4 3 2 2 2 acid 2C methylene disulfone5-6 4 4 3 3 1 3 2D methide acid 4-5 3 2 2 2 2 3 2E imide acid 5-6 3 4 43 2 2 2F ethylimide acid 5-6 3 3 4 2 2 2 2G trifluoromethanesulfonic 5-63 3 — 2 3 10  anhydride

Example 3

This example examines stability of a series of color changecyanoacrylates containing various ratios of triflic acid andmethanesulfonic acid. Two dye masterbatches were prepared employing thecomponents and quantities (in parts by weight) shown in Table 9 toprovide samples having acid/dye mol ratio of approximately 2/1 andcontaining approximately 3000 ppm dye. These dye masterbatches were thenblended with each other to provide the mol ratios of triflic acidcontent shown in Table 10 (in parts by weight).

TABLE 9 Dye Masterbatches MSA TFMSA Dye Base Example Acid PR01Concentrate Concentrate Concentrate A 3A-Master methanesulfonic acid9.54 0.213 — 0.3 (98%) 3E-Master trifluoromethanesulfonic 9.43 — 0.3330.3 acid

TABLE 10 Dye Master Batches Triflic Acid Content - Mol % Example3A-Master 3E-Master of Total Acid 3B-Master 3.75 1.25 0.25 3C-Master2.50 2.50 0.50 3D-Master 1.25 3.75 0.75

Five color change cyanoacrylate compositions were prepared from these 5dye masterbatches by blending 0.25 pt of each with 9.75 pt PR01 asdescribed in Example 1 to obtain samples containing approximately 75 ppmdye. The samples thus prepared were all deep blue in color and werechecked for set time then aged at room temperature and assessed after 16days for any change in color or viscosity. These results are presentedin Table 11, which show that stability increases, with respect to colorand viscosity, as the ratio of triflic acid/methane sulfonic acid in thesamples increases, i.e., as methanesulfonic acid, and so thenucleophilic anion content, decreases.

TABLE 11 Room Temperature Aged Color change Cyanoacrylate Triflic AcidContent - Initial Set 16 Day 16 Day Example Mol % of Total Acid Time(sec) Viscosity Color 3A 0.00 3 gel 0 3B 0.25 3 gel 0 3C 0.50 3 highvisc 1 3D 0.75 3 liquid 3 3E 1.00 2 liquid 3

Example 4

This example examines the effect of accelerant on the set time andbleaching speed of a color change cyanoacrylate. In this example 0.13 gdye masterbatch 3E-Master, having acid/dye mol ratio of approximately2/1 and containing approximately 3000 ppm dye Michler's hydrol cation,was added to a 5 g bottle of Scotch™ Super Glue Liquid and mixed well toobtain a deep blue colored sample containing approximately 75 ppm dye.The set time of this color change cyanoacrylate and an AD110 controlwere measured as described in the Test Method section with the exceptionthat the test was conducted on Lexan™ polycarbonate. The set time onpolycarbonate (hereinafter “PC”) was found to be quite long andprotracted, i.e., rather than the quick rigid set observed on glass; theset time on PC was more a continuum where the coupons could be movedeasily initially, then with more difficulty as viscosity increased, andfinally to a stiff stage where the coupons could still be moved butrequired significant force to move. In the time frame of 1-3 minutesafter bond closure increasing viscosity of the adhesive could bedetected, by 10-15 minutes the bond strength was building significantly,but the coupons could still be moved with moderate hand force. Probingof the bond strength was discontinued at 15 minutes. The dye-containingsample progressed toward cure slightly faster than did the controladhesive throughout all phases of cure. With respect to color changeduring the 15 minutes of observation, the bonded area of both samplesbecame cloudy, due to the PC imbibing the monomer, and slightly grey incolor, with the exception that the dye-containing sample was a lightblue-grey color. After standing for 16 hr in a constant temperature andhumidity room (CTH), at 22° C. and 50% RH, the samples appeared fullycured and the faint blue hue had vanished from the dye-containingsample.

The next experiment undertaken examined the effect of a cure acceleranton the cure speed of the dye-containing sample. One of the PC couponswas misted with Pronto™ Surface Activator, by depressing the spraybottle pump mechanism one time, and allowing the accelerator to dry fora few minutes. Cyanoacrylate was applied to the uncoated coupon and thebond was closed immediately. A set time of 3-4 seconds was recorded withthe sample bleaching colorless immediately upon cure. In this case thebonded area was clear and did not exhibit the cloudy appearance observedabove when no accelerator was employed. The above findings show that byemploying an appropriate accelerant, the set time and bleach speed on PCof colored cure indicating of the present disclosure can be reduced frommany minutes to a matter of seconds.

Example 5

This example examines the effect of dye concentration on set time andcolor stability of cyanoacrylate gel. The components employed to preparethe samples of this composition were dye masterbatch 3E-Master, havingacid/dye mol ratio of approximately 2/1 and containing approximately3000 ppm Michler's hydrol cation, and CA-50 gel, used in the proportions(in parts by weight) shown in Table 12. Sample 5D consisted of 1 ptsample 5A and 8 pt CA-50 gel and provided a dye content of approximately5 ppm. The samples were formulated by hand mixing, with a spatula, theappropriate ratio of gel and dye masterbatch, and transferring thehomogenous blue colored cure-indicating gel to a polypropylenecontainer. Sample color and set time were assessed using the testsdescribed in the Test Methods section and are presented in Table 12. Thedata show that the color intensity of the gels decreased with decreasingdye concentration. All of the samples bleached colorless during the settime test. A sample of the neat colorless gel was tested for set timeand found to have set time of 16 seconds, thus the presence of dye inExamples 5A to 5D did not slow the set time.

TABLE 12 Color Change Cyanoacrylate Gel Sample CA-50 3E- Dye Conc in SetTime ID Gel Master Gel (ppm) Color (Sec) 5A 9.85 0.1500 45 2.0 13 5B9.90 0.1000 30 1.5 13 5C 9.95 0.0500 15 1.0 12 5D — — 5 0.5 12

Example 6

This example examines the effect of acid/dye ratio on stability of colorchange cyanoacrylate compositions. In this series, dye concentratesconsisting of PR01, triflic acid, and Michler's hydrol were prepared bythe procedure described in Example 1 using the components in theproportions (in parts by weight) shown in Table 13 to obtain dyemasterbatches containing approximately 3000 ppm dye.

TABLE 13 Dye Masterbatches Acid/Dye Dye mol TFMSA Concentrate Sample IDRatio PR01 Concentrate A 6A-Master 2.5 9.36 0.416 0.3 6B-Master 2.0 9.430.333 0.3 6C-Master 1.5 9.51 0.250 0.3 6D-Master 1.0 9.58 0.167 0.3

The masterbatches of Table 13 were further formulated with PR01 toprovide the color change cyanoacrylates of Table 14 by combining 0.25 ptmasterbatch with 9.75 pt PR01, as described in Example 1, to obtainsamples containing approximately 75 ppm dye. Color and set time of thesamples were assessed as described in the Test Methods section and arereported in Table 14.

TABLE 14 Acid/Dye Ratios Masterbatch Acid/Dye Set Time Sample ID molRatio Color Set Time Bleach 6A 2.5 2.75 4 colorless 6B 2.0 2.75 5colorless 6C 1.5 3 5 colorless 6D 1.0 3 7 colorless

Example 7

This Example examines the effect of dye concentration on set time,color, and bleaching of color change cyanoacrylate compositions. In thisExample a dye masterbatch consisting of PR01, triflic acid, andMichler's hydrol was prepared by the procedure described in Example 1,employing 9.43 pt PR01, 0.333 pt TFMSA Concentrate, and 0.3 pt dye baseconcentrate A, to obtain dye masterbatches having an acid/dye mol ratioof approximately 2/1 and containing approximately 3000 ppm dye. The dyemasterbatches were further formulated with PR01 to provide the colorchange cyanoacrylates of Table 15 using the proportions (in parts byweight) disclosed therein. Color, set time, and bleaching of the sampleswere assessed as described in the Test Methods section and are reportedin Table 15. Samples 7D through 7F were considerably darker than thereference solutions, thus were labeled 3+. Set time results show that nocure inhibition is observed and that all the samples have essentiallythe same set time. All of the samples bleached colorless in the Set TimeTest.

TABLE 15 Dye Content Dye Set Set Time Sample (ppm) PRO-1 MasterbatchColor Time Bleach 7A 10 9.97 0.0333 2 5 colorless 7B 50 9.83 0.1667 2.755 colorless 7C 100 9.67 0.3333 3 5 colorless 7D 250 9.17 0.8333 3+ 5colorless 7E 500 8.33 1.6667 3+ 5-6 colorless 7F 1000 6.67 3.3333 3+ 4-6colorless

Examples 8 and 9

In these Examples two color change cyanoacrylate compositions wereprepared that changed from a first colored state to a second coloredstate, and did not exhibit the colored to colorless transition state,exhibited as the cyanoacrylate-based adhesive progresses from an uncuredstate to a cured state, of many of the previous examples. Example 8contained the bleachable dye of Michler's hydrol and the non-indicatordye 1,8-dihydroxyanthraquinone. Example 9 contained two color-changedyes, that of Michler's hydrol, and methyl yellow(4-(dimethylamino)azobenzene).

Example 8 employed two different dye solutions. The bleachable dyesolution was 3E-Master, containing triflic acid and Michler's hydrol inPR01 having an acid/dye mol ratio of 2/1 and a dye content of 3000 ppm.The non-bleachable dye solution contained 38.92 pt SB20 and 1.2 pt of a10% solution of 1,8-dihydroxyanthraquinone in methyl acetate, to providea non-indicating dye content of approximately 3000 ppm. To 9.67 pt ofthe non-bleachable dye solution was added 0.333 pt of 3E-Master, toprovide a bright green color change cyanoacrylate composition having a1,9-dihydroxyanthraquinone dye content of approximately 2900 ppm and aMichler's hydrol cation content of approximately 100 ppm. This samplewas tested for set time as described in the Test Methods section andprovided a set time of 1-2 seconds, which was the same as the parentSB20 adhesive. As this cyanoacrylate-based adhesive progressed from anuncured state to a cured state, the color changed almost instantaneouslyfrom green to bright yellow.

Example 9 employed two different dye solutions, both of which containedindicating dyes. The first dye solution consisted of the Michler'shydrol cation masterbatch of Example 1 based on PR01, triflic acid, andMichler's hydrol, and had an acid/dye mol ratio of approximately 2.2/1and a dye content of approximately 3000 ppm.

The second dye solution was prepared as in Example I by combining 9.25pt PR01, 0.2 pt TFMSA Concentrate, and 0.6 pt of a 5% solution of methylyellow in methyl acetate to provide a methyl yellow dye concentratehaving an acid to dye mol ratio of 1/1 and a dye content of 3000 ppm.

The adhesive composition was prepared by combining 8.08 pt PR01, 0.25 ptMichler's hydrol cation masterbatch, and 1.67 pt methyl yellow dyeconcentrate, to provide a color change cyanoacrylate compositioncontaining approximately 75 ppm Michler's hydrol and 500 ppm methylyellow. This sample was tested for set time as described in the TestMethods section and provided a set time of approximately 5 seconds,which was the same as the parent PR01 adhesive. As thiscyanoacrylate-based adhesive progressed from an uncured state to a curedstate, the color changed from an initial deep red color to anintermediate green and finally to a light orange color.

Example 10

This example demonstrates that a medical grade butyl cyanoacrylateadhesive can be converted to a color change adhesive composition byaddition of a Michler's hydrol dye masterbatch. The dye masterbatch andcolor change cyanoacrylate adhesive were prepared as described inExample I by first formulating a 10 wt % dye base solution of Michler'shydrol in methyl acetate and a 10 wt % acid solution of triflic acid inNexcare™ props Liquid Bandage (NDLB). The 10 wt % dye solution contained1.35 pt methyl acetate and 0.15 pt Michler's hydrol. The acid solutioncontained 1.8 pt NDLB and 0.2 pt triflic acid. The dye masterbatchcontained 9.46 pt NDLB, 0.30 pt 10% triflic acid solution, and 0.30 pt10% dye solution which resulted in a dye masterbatch having an acid/dyemol ratio of approximately 1.8/1 and a dye content of approximately 3000ppm dye.

The adhesive composition was prepared by combining 9.75 pt NDLB and 0.25pt dye masterbatch to provide a color change medical grade cyanoacrylateadhesive composition containing approximately 75 ppm dye. This deep bluesample was tested for set time as described in the Test Methods sectionand provided a set time of approximately 3-4 seconds, which was the sameas the parent NDLB adhesive. As this cyanoacrylate-based adhesiveprogressed from an uncured state to a cured state in the set time test,the color changed from an initial deep blue color to colorless. A dropof this adhesive composition was applied to the skin of a human hand,spread with a cotton-tipped applicator to provide a thin uniform layer,and observed for color change and set time. In approximately 1 minutethe adhesive bleached colorless and was dry to the touch.

Example 11

This example displays the Strength Ratio of a variety of acids withvarious nitrated aniline Acidity Indicators using the proceduresdescribed in the Test Methods section of this disclosure. The resultsare given in Table 16 and show the differentiation between workable andnonworkable acids in the instant invention.

TABLE 16 Strength Ratio of Various Acids (from Titration) StrengthWorkable Acid Indicator X Ratio E (Y/N) (CF₃SO₂)₂NH 2,6-dinitroaniline0.93 Y (C₂F₅SO₂)₂NH 2,6-dinitroaniline 0.93 Y CF₃SO₃H 2,6-dinitroaniline0.82 Y BF₃:2 acetic acid 2-chloro-6-nitroaniline 0.82 Y(CF₃SO₂)₃C⁻(H₂O)₁₆H⁺ 4-methoxy-2-nitroaniline 0.52 Y (CF₃SO₂)₂C(H)C₆H₅4-methoxy-2-nitroaniline 0.49 Y (CF₃SO₂)₂CH₂ 4-methoxy-2-nitroaniline0.34 Y BF₃:etherate 2-chloro-6-nitroaniline 0.30 Y (not buffered) BF₃:2CH₃OH 4-chloro-2-nitroaniline 0.24 Y Methanesulfonic acid4-chloro-2-nitroaniline <0.01 N Methanesulfonic acid 2,6-dinitroaniline<0.001 N Methanesulfonic acid 2-chloro-6-nitroaniline <0.001 N BF₃:2 H₂O4-chloro-2-nitroaniline 0.14 N CF₃CO₂H 4-methoxy-2-nitroaniline <0.01 N

Example 12

This example examines color change properties of various Michler'shydrol dye derivatives. Masterbatches of each dye are made by combining0.44 pt 10% solution of TFMSA in PR01 with 0.40 pt 10% solution of dyebase in THF and mixing well, followed by the addition of 9.16 pt PR01.The resulting dye masterbatches are agitated slowly for 30 minutes toassure homogeneity. Combining 4.91 pt PR01 with 0.094 pt dye masterbatchand agitating slowly for 30 minutes completes the preparation of colorchange cyanoacrylate samples. The resulting samples are tested byplacing 1 drop of color change cyanoacrylate on a first glass microscopeslide, placing a second glass slide atop the first and observing after 1minute to detect cure and note any color change that occurred.Inspecting the samples for cure reveals that all samples cure. Table 17provides the color change behavior.

TABLE 17 Bleach Behavior of Color Change Cyanoacrylate CompositionsInitial Color Sample Dye Name Color After Cure 12-1N-[bis[4-(dimethylamino)phenyl]- blue colorless methyl]-aniline 12-2N-[bis[4-(dimethylamino)phenyl]- blue colorlessmethyl]-N′-(4-ethoxyphenyl)-urea 12-3 N-[bis[4-(dimethylamino)phenyl]-blue colorless methyl]-N′-n-bulyl-urea 12-4N-[bis[4-(dimethylamino)phenyl]- blue colorless methyl]-N′-phenyl-urea12-5 N-[bis[4-(dimethylamino)phenyl]- blue colorless methyl]-morpholine12-6 N-[bis[4-(dimethylamino)phenyl]- light blue colorlessmethyl]-benzenesulfonamide 12-7 Bis[4-(4-morpholinyl)phenyl]methanolblue colorless 12-8 1,1-bis(4-dimethylaminophenyl)ethanol blue colorless12-9 1,1-bis(4-dimethylaminophenyl)- blue colorless ethylene  12-10bis(4-(dimethylamino-2-methylphenyl)- blue colorless methanol  12-11bis(3-bromo-4-dimethylaminophenyl)- blue colorless methanol

Example 13

This Example examines the effect of acid/dye mol ratio on the behaviorof color change cyanoacrylate adhesives. The acids examined wereBF₃:2CH₃OH, BF₃(AcOH)₂, and imide acid at acid/dye mol ratios rangingfrom 1:1 to 5:1. For the two BF₃-complexes, the acid/dye mol ratio wasbased on mols BF₃, not mols of the BF₃-complexes. Acid/dye masterbatcheswere formulated by preparing 10 wt % solutions of each acid in SB14 andcombining these acid concentrates with Dye Base Concentrate A and SB14in the ratios shown in Table 18. Specifically, Dye Base Concentrate Awas added to acid concentrate and mixed well before SB14 was added andmixed to complete preparation of the acid/dye concentrates. Mixing 0.25parts of acid/dye concentrate with 9.75 pt SB14 in HDPE bottlescompleted preparation of the color change cyanoacrylate adhesives.

TABLE 18 Acid/Dye Concentrates Acid/Dye Dye Base Sample Acid mol RatioSB14 Conc A Acid Conc 13-1-AD BF₃(AcOH)₂ 1.00 9.210 0.3 0.578 13-2-ADBF₃(AcOH)₂ 2.00 8.690 0.3 1.155 13-3-AD BF₃(AcOH)₂ 3.00 8.170 0.3 1.73313-4-AD BF₃(AcOH)₂ 4.00 7.650 0.3 2.311 13-5-AD BF₃(AcOH)₂ 5.00 7.1300.3 2.889 13-6-AD BF₃•2CH₃OH 1.00 9.595 0.3 0.150 13-7-AD BF₃•2CH₃OH2.00 9.459 0.3 0.301 13-8-AD BF₃•2CH₃OH 3.00 9.324 0.3 0.451 13-9-ADBF₃•2CH₃OH 4.00 9.188 0.3 0.602 13-10-AD BF₃•2CH₃OH 5.00 9.053 0.3 0.75213-11-AD Imide Acid 1.00 9.449 0.3 0.312 13-12-AD Imide Acid 2.00 9.1680.3 0.624 13-13-AD Imide Acid 3.00 8.888 0.3 0.936 13-14-AD Imide Acid4.00 8.607 0.3 1.248 13-15-AD Imide Acid 5.00 8.326 0.3 1.560

Sample 13-6, based on BF₃:2CH₃OH and having acid/dye mol ratio of 1:1,gelled shortly after preparation, and Sample 13-11, based on imide acidand having an acid/dye mol ratio of 1:1 gelled sometime between 1 and 2weeks while aging at room temperature. The color stability of theadhesives was assessed after aging them for various lengths of time atroom temperature as shown in Table 19. For each acid, increased acid/dyeratios resulted in increased bleach times.

TABLE 19 Color of Color Change CA Adhesives Aged at Room TemperatureAcid/Dye 1 Week 2 Week 3 Week Sample Acid mol Ratio Color Color Color13-1 BF₃(AcOH)₂ 1.00 2.75 2.75 2.75 13-2 BF₃(AcOH)₂ 2.00 2.75 2.5 2.513-3 BF₃(AcOH)₂ 3.00 2.75 2.5 2.5 13-4 BF₃(AcOH)₂ 4.00 2.5 2.25 2.2513-5 BF₃(AcOH)₂ 5.00 2.5 2.25 2.25 13-6 BF₃:2CH₃OH 1.00 — — — 13-7BF₃:2CH₃OH 2.00 2.75 2.5 2.25 13-8 BF₃:2CH₃OH 3.00 2.75 2.5 2.25 13-9BF₃:2CH₃OH 4.00 2.75 2.5 2.25 13-10 BF₃:2CH₃OH 5.00 2.75 2.75 2.5 13-11Imide Acid 1.00 — — — 13-12 Imide Acid 2.00 2.75 3 2.75 13-13 Imide Acid3.00 2.25 2.5 2.25 13-14 Imide Acid 4.00 2 2 2 13-15 Imide Acid 5.00 1.51.5 1.5

The present invention should not be considered limited to the particularexamples described above, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention may be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the instant specification.

1-21. (canceled)
 22. A cyanoacrylate-based adhesive compositioncomprising: a cyanoacrylate monomer; and a bleachable dye comprisingMichler's hydrol cation, or derivatized Michler's hydrol cation, pairedwith a non-nucleophilic anion that provides a stable color to thecyanoacrylate-based adhesive.
 23. A cyanoacrylate-based adhesivecomposition according to claim 22 wherein the bleachable dye isMichler's hydrol cation.
 24. A cyanoacrylate-based adhesive compositionaccording to claim 22 wherein the non-nucleophilic anion is derived froma carbon-acid having a strength ratio value greater than 0.1 whenmeasured in sulfolane solvent and using 4-methoxy-2-nitroanilineindicator.
 25. A cyanoacrylate-based adhesive composition according toclaim 22 wherein the non-nucleophilic anion is derived from anon-carbon-acid having a strength ratio value greater than 0.2 whenmeasured in sulfolane solvent and using 4-chloro-2-nitroanilineindicator.
 26. A cyanoacrylate-based adhesive composition according toclaim 22 wherein the non-nucleophilic anion is derived from borontrifluoride methanol, trifluoromethanesulfonic acid, methide acid, imideacid, ethylimide acid, boron trifluoride acetic acid, or mixturesthereof.
 27. A cyanoacrylate-based adhesive composition according toclaim 22 wherein the Michler's hydrol cation or derivatized Michler'shydrol cation is present in the cyanoacrylate-based adhesive in at least1 ppm and the non-nucleophilic anion is present in thecyanoacrylate-based adhesive at a non-nucleophilic anion/dye mol ratioof 1 to
 5. 28. A cyanoacrylate-based adhesive composition according toclaim 22 further comprising a colorant.
 29. A method comprising:combining a cyanoacrylate monomer with a bleachable dye comprising aMichler's hydrol cation, or derivatized Michler's hydrol cation, pairedwith a non-nucleophilic anion to form a dye pair, the dye pair having astable color, the cyanoacrylate monomer and dye pair forming acyanoacrylate-based adhesive composition.
 30. A method according toclaim 29 further comprising curing the cyanoacrylate-based adhesivecomposition to form a colorless or light-colored curedcyanoacrylate-based adhesive composition.
 31. A method according toclaim 29 further comprising combining a colorant with the cyanoacrylatemonomer, and dye pair to provide a stable altered color to thecyanoacrylate-based adhesive composition.
 32. A method according toclaim 31 further comprising curing the cyanoacrylate-based adhesivecomposition to form a cured cyanoacrylate-based adhesive compositionhaving a second color being different than the stable altered color andstable color.
 33. A method according to claim 29 further comprisingcomparing the color of the cyanoacrylate-based adhesive composition witha reference color chart to determine a change in the cyanoacrylate-basedadhesive composition.
 34. A method according to claim 29 furthercomprising disposing the dye pair on a substrate before the combiningstep.
 35. A method according to claim 29 further comprising disposingthe cyanoacrylate-based adhesive composition on a substrate and curingthe cyanoacrylate-based adhesive composition to a colorless orlight-colored cured cyanoacrylate-based adhesive composition.
 36. Amethod according to claim 29 wherein the non-nucleophilic anion isderived from a carbon-acid having a strength ratio value greater than0.1 when measured in sulfolane solvent and using4-methoxy-2-nitroaniline indicator.
 37. A method according to claim 29wherein the non-nucleophilic anion is derived from a non-carbon-acidhaving a strength ratio value greater than 0.2 when measured insulfolane solvent and using 4-chloro-2-nitroaniline indicator.
 38. Amethod according to claim 29 wherein the non-nucleophilic anion isderived from boron trifluoride methanol, trifluoromethanesulfonic acid,methide acid, imide acid, ethylimide acid, boron trifluoride aceticacid, or mixtures thereof.
 39. A method according to claim 35 furthercomprising applying a surface activator to the substrate prior to thedisposing step.
 40. A method according to claim 29 wherein thenon-nucleophilic anion is added to the Michler's hydrol cation orderivatized Michler's hydrol cation in a mol ratio of non-nucleophilicanion/dye range from 1 to 5 and the Michler's hydrol cation orderivatized Michler's hydrol cation is present in thecyanoacrylate-based adhesive composition of at least 1 ppm.
 41. A methodaccording to claim 29 further comprising waiting 14 days after thecombining step and then visually confirming that the color persists.